Factors affecting callus production and glycosidal content of leaf tissue culture of Digitalis lanata Ehrh

Grecian Foxglove, Digitalis lanata Ehrh. (Scrophulariaceae), is a perennial or biennial plant, which is a major source of digoxin and digitoxin. Its leaves are used for the preparation of these cardiac active glycosides for the treatment of cardio vascular disorders. This study was built on a suggestion that in Digitalis the explanted cells already contain all the genetic information that is required for the manufacture of digitoxin and digoxin. Accordingly, this genetic information will be present in callus from explant micro-culture. Activation by external factors such as light, the number of sub-cultures and type and age of the explants, should lead to stimulation, not only of callus size, but also the production of glycosides. Segments of series explants taken from different Digitalis plant organs (shoot tip, leaf, hypocotyl and root), 2 and 4 weeks old, obtained from plants grown in vitro and of 8, 12 and 20 weeks from plants cultivated in vivo culture, were cultured on aseptic MS basal solid medium containing 5.0 mg/L 2.4-D and 0.5 mg/L BA. On the other hand, callus derived from different explants was recultured (in initial amounts of 49 – 63 mg) on the same new sterilised MS medium in order to increase the mass of callus. The cultures were then maintained in a growth chamber at 26° ± 2 C° and subjected to four different light photoperiods as follows: 10 hr. light /14 hr. dark cycle, 14 hr. light/10 hr. dark cycle, 16hr.light/ 8hr.dark cycle, and 18 hr. light/ 6 hr. dark cycle. The obtained results show that the greatest callus production, as well as the highest amount of glycosides, occurred in callus derived from 2 or 20 week old leaf explants among all the examined types and ages of explants. Repeating the subculturing three times decreased dramatically the dry weight of callus, but it significantly favoured digoxin and digitoxin content. The optimal callus growth was obtained at 16 hr. light/day but the best glycosidal content was achieved when callus was exposed to 18hr. light/day.